1. Field of the Invention -- This invention relates to a vehicle diagnostic system, and particularly to an apparatus and method for determining the speed (rpm), dwell and timing of an internal combustion engine, as well as cylinder power contribution and distributor condition. Accurate information of these parameters is essential for tuning an engine to obtain maximum efficiency and minimum pollutant emissions, as well as for performing additional tests on the vehicle operation.
2. Description of the Prior Art -- Motor vehicles are increasing in number, type and complexity. At the same time, mechanics who are adequately trained and technically up-to-date are becoming harder to find. Consequently, when vehicles are taken to a garage or service station for repairs, owners are faced with faulty or incomplete diagnosis, unnecessary replacements, return visits and dissatisfaction; dealers and manufacturers are faced with high warranty costs; and owners and fleet operators are faced with excessive vehicle downtime and higher than necessary repair costs.
In an attempt to reduce the problems associated with motor vehicle repairs, automated vehicle diagnostic systems are being developed which will permit diagnosis of vehicle condition by relatively unskilled personnel. Many such diagnostic systems simply display vehicle test parameters such as by oscilloscope waveforms or print-outs. Other diagnostic systems compare the vehicle test parameters with specification data supplied by the manufacturer. In both cases there is no attempt to diagnose a vehicle malfunction, and the analysis of the test data and determination of the required repair, if any, is left to the judgment of the mechanic or test operator. While such systems are satisfactory for obvious vehicle faults such as a defective cylinder, the output data is still subject to erroneous analysis and may result in unnecessary repairs.
Recently there has been developed a completely automated vehicle diagnostic system which not only displays the vehicle performance data and any deviations from vehicle specifications, but also diagnoses the malfunction and informs the test operator of the required repairs. This system, known as AUTOSENSE.sup.TM completely eliminates guesswork and unnecessary repairs, and the system can be used after the repairs are made to insure that the vehicle has been properly repaired.
The present invention forms a portion of the AUTOSENSE vehicle diagnostic system, and provides to the system signals indicative of vehicle rpm, and ignition system dwell and timing, as well as indicating distributor mechanical condition and the power contributed by each cylinder. These parameters are fundamental in determining the condition of the vehicle engine and ignition system, and knowledge of one or more of these parameters is necessary to determine other vehicle conditions.